C16 and C24 are strength grades; the higher the grade, the better the load bearing quality it has. C16 is normally the grade that is produced from faster grown UK timber. C24 is a premium product as the wood is slower grown and is also denser. Higher loads and longer spans can be achieved with the use of C24 grade timber often with a smaller cross section. The majority of grading is now performed by machines with x-ray scanning and imaging technology to ensure the timber is within grading guidelines. Timber can also be graded visually by qualified visual timber graders who assess size, frequency and distribution, shakes, splits and slope of grain. This ensures only the pieces that meet standard limitations are accepted as a grade pass. Regularised timber has gone through a machine which rounds the edges and smooths the faces and sides of the piece. This operation uniforms the finished size which will usually be 5mm less than stated on both the face and width.
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